1. Field of the Invention
The present invention relates to an image heating apparatus for heating an image formed on a recording material. This image heating apparatus includes, as examples, a fixing apparatus used for an image forming apparatus such as a copy machine, a facsimile, a printer, and the like.
2. Related Background Art
An electrophotographic type image forming apparatus such as a copy machine, a printer, etc. has a fixing apparatus for heating, melting, and then fixing a not-yet-fixed toner image, which is formed corresponding to an image information, on to a recording material such as a plain paper, a coated paper, an OHP sheet, and the like.
As disclosed in Japanese Patent Application Laid-Open No. 2001-201979, there has been known a belt-nip type fixing apparatus which causes a pressure body to pressure-contact a fixing rotational member with heating means, and causes a recording material to pass through a fixing nip mentioned below. Thereby not-yet-fixed toner image formed on the recording material is fixed. The pressure body is constituted by an endless belt rotatably engaged with a plurality of supporting rollers, a pressure member fixedly disposed inside of the endless belt so as to pressure-contact the endless belt toward the fixing rotational member from inside. The above-mentioned fixing nip is formed between the fixing rotational member and the pressure member (between the fixing rotational member and the endless belt pressure-contacting the pressure member).
In a case where the above-mentioned image forming apparatus continuously forms the image on the recording material, the recording material passes through the fixing nip, which is formed between the fixing rotational member and the endless belt, with a predetermined interval (hereinafter referred to as “the interval-between-papers”. To this end, during the interval-between-papers in which the recording material is not within the fixing nip, the endless belt undergoes a surplus heat from the fixing rotational member, so that the temperature increases all over the endless belt too much, which may unfavorably lead to a disturbance of the not-yet-fixed toner image formed on the recording material.
Further, when the recording material continuously passing therethrough has a width less than the maximum width (the maximum length with respect to a direction perpendicular to the conveying direction) of the recording material which is capable of passing through the fixing nip, the endless belt rises in temperature much higher at its non-sheet-passing portion than at its sheet-passing portion, thereby causing a surface of the endless belt to be subjected to a temperature unevenness with respect to its longitudinal direction (a width direction perpendicular to the conveying direction). This may lead an evenness of temperature melting the not-yet-fixed toner image to thereby deteriorate the image, or an evenness of a friction coefficient of the fixing nip to thereby deteriorate the image. Such a problem relating to a false image occurs markedly in the case of the recording material of a coated paper, a thick paper, or the like.
To the above-mentioned image deterioration due to the endless belt rising in temperature too much, a cooling apparatus such as a blower fan, and the like is conventionally disposed in the vicinity of the endless belt to thereby forcibly cool the endless belt, as shown in Japanese Patent Application Laid-Open No. 2001-201979.
However, in these days, the image forming apparatus is required for the speeding up and the miniaturization space-saving, which causes the fixing apparatus and the image forming apparatus to come close to each other. In the construction disclosed in Japanese Patent Application Laid-Open No. 2001-201979, hot air of the fixing apparatus reaches the image forming unit being a peripheral member of the fixing apparatus, which provides another problem such as a blocking, and the like, in which the toner on the photosensitive drum in the image forming unit unfavorably melts and hence adheres thereto.